#include<stdio.h>
int main()
{
	int i = 0;
	int arr[] = { 1,2,3,2,1 };
	int len = sizeof(arr) / sizeof(arr[0]);
	int sum = 0;
	for (i = 0; i < len; i++)
	{
		sum ^= arr[i];
	}
	printf("%d\n", sum);
	return 0;
}